Cellular Carriers that support the Apple Watch, which models, the radio frequencies each model uses, and the country where they offer service:
https://www.apple.com/watch/cellular
The carrier has to support the Apple Watch, because it needs to be able to share the iPhone’s phone number with the Apple Watch.
If the carrier ia not in the list, it most likely does not support the Apple Watch.
The GPS only Apple Watch can do Everything the cellular model can do as long as your iPhone is nearby.
What the Apple Watch GPS-only can do without an iPhone (there is information about the cellular model as well)
https://support.apple.com/en-us/HT205547
https://www.imore.com/heres-what-apple-watch-can-do-without-iphone